High-risk male-to-female transgender women (hereafter transwomen) face numerous concurrent cofactors for HIV acquisition and transmission including substance use, engagement in sex work, unemployment, low educational attainment, homelessness and hormone misuse. In Los Angeles County, estimates of HIV prevalence among transwomen are 15% overall, and 17% among Latinas, 29% among Native Americans, and 48% among African American/black transwomen. As a result of discrimination/stigma, prejudice, and individual and structural forms of transphobia, transwomen form dense communities comprised primarily of other transwomen. Transwomen use social network sites (SNS) and technology-based (tech) networking platforms to develop social support structures, connect with members of their community, receive positive and re- affirming perspectives on their gender identity, and inform behavioral norms and gain access to transgender specific resources (e.g., illegal hormones, sex work partners). In response to PA-12-113, Research on the Health of LGBTI Populations, and consistent with the priorities for behavioral and social sciences outlined in the HIV-Related Research Plan put forward by the Office of AIDS Research of the National Institutes of Health and the Trans-NIH plan for 2014, this proposed project seeks to conduct formative research to examine how the egocentric structure and composition of transwomens' social networks and SNS/tech use affect their engagement in HIV risk/protective behaviors. During Phase 1, focus groups will be conducted to guide the development of culturally competent assessments (an iPad Social Network Interview [SNI] and ACASI), which will then undergo a feasibility pilot test. During Phase 2, a diverse sample of transwomen (N=300) will be recruited to complete the two-part assessment. The specific aims of this research are: 1) Develop and assess the feasibility and utility of culturally competent assessments to study the social networks, HIV risk/protective behaviors, and SNS/tech use of transwomen; 2) Determine how characteristics of transwomen's social networks, as well as the behavior of other people (i.e., alters) in those networks, influence engagement in HIV risk/protective behaviors; and, 3) Determine how SNS/tech use with network alters influences participants' engagement in HIV risk/protective behaviors. Statistical analyses will use hierarchically clustered models that nest participants within their reported social networks. The proposed research will specify the social network dynamics driving transwomen's HIV risk/protective behaviors to inform the development a R34 application to test the efficacy of a culturally competent SNS/tech-based HIV intervention tailored specifically for transwomen.